Fescue Grasses
Fescue grasses (Festuca species) are widely used as turf in a variety of applications, including home lawns, golf courses, athletic fields, parks, pasture and along roadsides. Two types of fescue grasses are most commonly grown: tall fescues and fine fescues. Tall fescue grasses (such as F. arundinacea) have excellent drought and wear resistance. Tall fescue is adapted to a wide range of climactic conditions and is the most predominant cool-season, perennial grass in the United States. (See Tall Fescue, Edited by R. C. Buckner and L. P. Bush, Published by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. ASA Monograph Number 20. 1979. ISBN 0-89118-057-5). The term fine fescue encompasses several subtypes including hard fescue grasses (F. longifolia); these grasses are low maintenance and shade tolerant, but lack the durability of the tall fescue grasses.
Glyphosate Herbicides
Glyphosate (N-(phosphonomethyl) glycine) is the active ingredient in glyphosate herbicides, such as ROUNDUP.RTM. brand herbicide produced by Monsanto, St. Louis, Mo. Typically, glyphosate is formulated as a water-soluble salt such as an ammonium, alkylamine, alkali metal or trimethylsulfonium salt. One of the most common formulations is the isopropylamine salt of glyphosate, which is the form employed in ROUNDUP.RTM. brand herbicide.
Glyphosate is a broad spectrum herbicide that inhibits the enzyme enolpyruvylshikimate-phosphate synthase (ESPS). It is conventionally applied as an aqueous solution to the foliage of plants, where it is taken up into the leaves and transported throughout the plant. Commercial formulations of glyphosate may also include one or more surfactants to facilitate penetration of the active ingredient into the plant leaves, as well as compounds to enhance rainfastness. Numerous U.S. patents have been issued that disclose various formulations of glyphosate, including U.S. Pat. Nos. 4,405,531; 5,118,338; 5,196,044; 5,639,711; 5,652,197; 5,679,621; and 5,750,468.
Little success has been reported in finding natural resistance to glyphosate herbicides in plants. This is beneficial in one respect since it indicates that the likelihood of glyphosate resistant populations of weeds arising is low, but it also means that no naturally resistant desirable plant species are available. As a result, great care must be taken when applying glyphosate herbicides in the vicinity of desirable plants (e.g., crops, ornamentals, grass turf). In order to increase the utility of glyphosate herbicides in crop species, a bacterial gene conferring glyphosate resistance has been introduced into a few crops, including soybean and corn (see U.S. Pat. Nos. 5,188,642; 5,463,175; 5,554,798; and 5,633,448). Weed growth in these transgenic crops may be controlled by application of glyphosate herbicides, without significantly adversely affecting the growth of the crop.
Glyphosate herbicides are highly effective against grass species, and so cannot be effectively applied to control weed growth in turf grasses. The production of transgenic grasses harboring a bacterial glyphosate resistance gene is hampered by the lack of reliable transformation procedures for grass species. It is also likely that public acceptance of transgenic grasses for widespread domestic use (for example, in home lawns) would be difficult.